Solid adsorbents are commonly used to remove contaminants from hydrocarbon streams such as olefins, natural gas and light hydrocarbon fractions. Since these streams can contain different contaminants, more than one adsorbent or adsorbent bed may be needed to sufficiently purify the stream so that it can be used in the desired process. Contaminants which can be present in these streams include chlorides, H2O, CO, O2, CO2, COS, H2S, NH3, AsH3, PH3, Hg, methanol, mercaptans and other S- or O-containing organic compounds.
Aromatics extraction units which may accept a feed for a continuous catalytic reforming platforming unit may have corrosion problems caused by chloride ingress and accumulation of chlorides in the solvent. Current methods for chloride removing using solid adsorbents is practiced in the art, however it is an expensive option because a large heavy hydrocarbon containing stream must be treated in order for the method to be effective.
For example, a refiner extracting benzene from a reformed stream may apply a chloride removal bed on the feed to the benzene extraction unit. The chloride removal bed may be applied since chlorides in the feed to the unit may have been contributing to corrosion issues in the unit. However, once the chloride removal bed was applied to the feed, the corrosion issues of the unit were improved as indicated by the pH control of the process streams, more specifically, areas of acidity were greatly improved. Using this placement, over time the unit begins to have problems with recovery of the benzene. The poor recovery of benzene is assigned to a buildup of heavy oil in the solvent of the unit causing the solvent to be less effective. The adsorbent acts as a catalyst for acid catalyzed reactions such as alkylation of aromatic hydrocarbons with olefins. The catalytic action of the adsorbent is even more enhanced upon adsorption of chloride contaminants. The side reaction of alkylation described above leads to substantial increase of the molecular weight of the feeds, sometimes by factor of two or even more. This high molecular weight material built up in the unit is detrimental as the unit is not designed to handle this material.
Therefore, there is a need for a process using a reasonably sized and properly located chloride removal bed.